1. Field of the Invention
This invention relates to a suspension system for use in a yard tractor having a tiltable cab hinged at the front in which the cab has an offset center of gravity. More particularly, the invention is concered with a suspension system disposed between the frame of the tractor and the cab at the rearward side of the cab including a pair of air sleeve springs in which one of the springs is larger than the other and disposed on the side of the cab with the center of gravity.
2. Description of the Prior Art
Yard tractors are used for towing semi-trailers in freight yards in order to position the semi-trailers and container chassis for loading and unloading. Normally, yard tractors are not used for "over the road" transport of semi-trailers.
Typically, a yard tractor includes a tiltable cab hinged near the forward end of the cab which is raised to gain access to the engine and lowered by the use of a hydraulic cylinder coupled between the frame and the cab. Because a yard tractor is normally used only for short distances, a typical yard tractor makes provisions for only one person--the driver--and the cab is configured so that the driver's compartment is disposed to either side of the cab. Because of this, the cab has a center of gravity offset from the longitudinal centerline of the cab.
Conventional tiltable yard tractor cabs are coupled directly to the frame of the tractor with little or no provision for resilient suspension between the cab and the frame. As a result, the driver of the cab is subjected to a very uncomfortable ride because freight yards typically have many bumps and potholes.
It is known in the art to provide an air sleeve spring suspension system for over-the-road tractors which have a balanced symmetrical cab--that is, a cab providing for a driver and a passenger. In such prior art systems having tiltable cabs, it is known to provide a pair of air sleeve springs coupled between the rearward side of the cab and the frame in order to provide a more comfortable "cushioned" ride for the occupants of the cab. These prior art systems, however, would be inadequate for a yard tractor because they do not compensate for the offset center of gravity. If such a prior art system were used on a yard tractor having an offset center of gravity, the cab would tilt to one side because of the unbalanced load.
Additionally, known prior art air sleeve suspension systems couple the air sleeve springs to the cab which results in a mechanically complex system requiring manually disconnecting to tilt the cab.